President Trump on Wednesday signed a travel ban on 12 countries, primarily in Africa and the Middle East, reviving an effort from his first term to prevent large numbers of immigrants and visitors from entering the United States.

Here is a closer look at why the administration says it is instituting full bans on foreign nationals traveling to the U.S. from 12 nations.

The ban that takes effect Monday blocks travelers from 12 countries, primarily in the Middle East and Africa, including Afghanistan, Iran and Yemen, from entering the United States. Additionally,